U.S. patent number 9,555,869 [Application Number 14/610,377] was granted by the patent office on 2017-01-31 for systems and methods for setting engine speed in a marine propulsion device.
This patent grant is currently assigned to Brunswick Corporation. The grantee listed for this patent is Brunswick Corporation. Invention is credited to Steven J. Andrasko, Jason S. Arbuckle, Kenneth G. Gable, William P. O'Brien, Andrew J. Przybyl, Gene A. Smedema, David M. Van Buren.
United States Patent |
9,555,869 |
Arbuckle , et al. |
January 31, 2017 |
Systems and methods for setting engine speed in a marine propulsion
device
Abstract
A method for setting an engine speed of an internal combustion
engine in a marine propulsion device of a marine propulsion system
to an engine speed setpoint includes determining the engine speed
setpoint based on an operator demand and predicting a position of a
throttle valve that is needed to achieve the engine speed setpoint.
The method also includes determining a feed forward signal that
will move the throttle valve to the predicted position, and after
moving the throttle valve to the predicted position, adjusting the
engine speed with a feedback controller so as to obtain the engine
speed setpoint. An operating state of the marine propulsion system
is also determined. Depending on the operating state, the method
may include determining limits on an authority of the feedback
controller to adjust the engine speed and/or determining whether
the operator demand should be modified prior to determining the
engine speed setpoint.
Inventors: |
Arbuckle; Jason S. (Horicon,
WI), Andrasko; Steven J. (Oshkosh, WI), Przybyl; Andrew
J. (Berlin, WI), O'Brien; William P. (Eden, WI),
Gable; Kenneth G. (Oshkosh, WI), Van Buren; David M.
(Fond du Lac, WI), Smedema; Gene A. (Princeton, WI) |
Applicant: |
Name |
City |
State |
Country |
Type |
Brunswick Corporation |
Lake Forest |
IL |
US |
|
|
Assignee: |
Brunswick Corporation (Lake
Forest, IL)
|
Family
ID: |
57867433 |
Appl.
No.: |
14/610,377 |
Filed: |
January 30, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B63H
21/213 (20130101); F02D 29/02 (20130101); F02B
61/045 (20130101); F02D 11/106 (20130101); F02D
41/107 (20130101); F02D 9/08 (20130101); F02D
41/1401 (20130101); B63H 21/14 (20130101); F02D
2200/60 (20130101); F02D 2041/141 (20130101); B63H
2021/216 (20130101); F02D 41/2422 (20130101); F02D
2200/0404 (20130101) |
Current International
Class: |
F02D
11/10 (20060101); B63H 21/21 (20060101); F02D
9/08 (20060101); B63H 21/14 (20060101) |
Field of
Search: |
;701/85,110
;123/319,327,339.12,339.15,339.16,339.19,339.23,344,352,3,99 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Newport, Motion Control Coordinate System, www.newport.com, pp. 7-2
through 7-25, website visited Nov. 18, 2014. cited by applicant
.
Mercury Marine, SmartCraft Manual, p. 11, May 2012. cited by
applicant .
U.S. Appl. No. 14/104,291, filed Dec. 12, 2013. cited by applicant
.
U.S. Appl. No. 14/284,795, filed May 22, 2014. cited by applicant
.
U.S. Appl. No. 14/573,202, filed Dec. 17, 2014. cited by applicant
.
Beauregard, Brett, "Improving the Beginner's PID: Reset Windup",
Project Blog,
http://brettbeauregard.com/blog/2011/04/improvingthebeginner%E2%80%-
99spidresetwindup/, website visited Jul. 20, 2016, available at
least as early as Jul. 22, 2011. cited by applicant.
|
Primary Examiner: Kwon; John
Assistant Examiner: Hoang; Johnny H
Attorney, Agent or Firm: Andrus Intellectual Property Law,
LLP
Claims
What is claimed is:
1. A method for setting an engine speed of an internal combustion
engine in a marine propulsion device of a marine propulsion system
to an engine speed setpoint, the method comprising: determining the
engine speed setpoint based on an operator demand; predicting a
position of a throttle valve of the engine that is needed to
achieve the engine speed setpoint; determining a feed forward
signal that will move the throttle valve to the predicted position;
after moving the throttle valve to the predicted position,
adjusting the engine speed with a feedback controller so as to
obtain the engine speed setpoint; and determining an operating
state of the marine propulsion system, wherein depending on the
operating state, the method further comprises: determining limits
on an authority of the feedback controller to adjust the engine
speed, wherein the authority limits comprise at least one of
maximum and minimum proportional term limits and maximum and
minimum integral term limits; and determining whether the operator
demand should be modified prior to determining the engine speed
setpoint when the operating state is a joysticking mode or a
throttle-only mode.
2. The method of claim 1, wherein the operating state comprises
operation in an operator-selected control mode, and further
comprising selecting the authority limits based on the
operator-selected control mode.
3. The method of claim 2, further comprising waiting to switch from
a first operator-selected control mode to a second
operator-selected control mode until the operator demand is less
than an upper demand limit associated with the second
operator-selected control mode.
4. The method of claim 1, wherein the operating state comprises
operation in the joysticking mode, in which a direction and a
magnitude of thrust of the marine propulsion device are determined
based on a position of a joystick.
5. The method of claim 4, further comprising modifying the operator
demand prior to determining the engine speed setpoint to account
for one of a gear ratio and a pitch of a propeller of the marine
propulsion device when the marine propulsion system is operating in
the joysticking mode.
6. The method of claim 1, wherein the operating state comprises
operation in the throttle-only mode, in which the operator demand
can be varied while a transmission of the marine propulsion system
is in neutral.
7. The method of claim 6, further comprising determining whether
the operator demand exceeds a predetermined threshold when the
marine propulsion system is operating in the throttle-only mode,
and if so, modifying the operator demand by capping it at the
predetermined threshold prior to determining the engine speed
setpoint.
8. The method of claim 7, further comprising multiplying the feed
forward signal by a fractional gain when the marine propulsion
system is operating in the throttle-only mode.
9. The method of claim 1, wherein the operating state comprises one
of acceleration of the engine speed and deceleration of the engine
speed.
10. The method of claim 9, further comprising calculating a demand
delta between a current operator demand and a previous operator
demand, and using the demand delta and the engine speed setpoint to
determine the authority limits.
11. The method of claim 10, further comprising filtering the
previous operator demand to the current operator demand such that
the demand delta progressively decreases, and using the decreasing
demand delta and the engine speed setpoint to determine the
authority limits.
12. The method of claim 11, further comprising providing the
feedback controller with less authority to adjust the engine speed
during deceleration of the engine speed than during acceleration of
the engine speed.
13. The method of claim 11, further comprising providing the
feedback controller with increasingly more authority to adjust the
engine speed as the demand delta progressively decreases.
14. A marine propulsion system for setting an engine speed of an
internal combustion engine in a marine propulsion device to an
engine speed setpoint, the system comprising: a throttle valve
controlling an amount of air provided to the engine; an input
device for inputting an operator demand; an electronic control unit
that determines the engine speed setpoint based on the operator
demand, predicts a position of the throttle valve that is needed to
achieve the engine speed setpoint, and determines a feed forward
signal that will move the throttle valve to the predicted position;
and a feedback controller that adjusts the engine speed so as to
obtain the engine speed setpoint after the throttle valve has been
moved to the predicted position; wherein the electronic control
unit determines an operating state of the marine propulsion system;
and wherein depending on the operating state, the electronic
control unit further determines: limits on an authority of the
feedback controller to adjust the engine speed, wherein the
authority limits comprise at least one of maximum and minimum
proportional term limits and maximum and minimum integral term
limits; and whether the operator demand should be modified prior to
determination of the engine speed setpoint when the operating state
is a joysticking mode or a throttle-only mode.
15. The marine propulsion system of claim 14, wherein the operating
state comprises operation in an operator-selected control mode, and
wherein the electronic control unit selects the authority limits
based on the operator-selected control mode.
16. The marine propulsion system of claim 15, wherein the
electronic control unit prevents a switch from a first
operator-selected control mode to a second operator-selected
control mode until the operator demand is less than an upper demand
limit associated with the second operator-selected control
mode.
17. The marine propulsion system of claim 14, wherein the input
device comprises a joystick, and wherein the operating state
comprises operation in the joysticking mode, in which a direction
and a magnitude of thrust of the marine propulsion device are
determined based on a position of the joystick.
18. The marine propulsion system of claim 17, wherein the
electronic control unit modifies the operator demand prior to
determining the engine speed setpoint to account for one of a gear
ratio and a pitch of a propeller of the marine propulsion device
when the marine propulsion system is operating in the joysticking
mode.
19. The marine propulsion system of claim 14, wherein the operating
state comprises operation in the throttle-only mode, in which the
input device can be used to vary the operator demand while a
transmission of the marine propulsion system is in neutral.
20. The marine propulsion system of claim 19, wherein the
electronic control unit determines whether the operator demand
exceeds a predetermined threshold when the marine propulsion system
is operating in the throttle-only mode, and if so, modifies the
operator demand by capping it at the predetermined threshold prior
to determining the engine speed setpoint.
21. The marine propulsion system of claim 14, wherein the operating
state comprises one of acceleration of the engine speed and
deceleration of the engine speed.
22. The marine propulsion system of claim 21, wherein the
electronic control unit calculates a demand delta between a current
operator demand and a previous operator demand, and uses the demand
delta and the engine speed setpoint to determine the authority
limits.
23. The marine propulsion system of claim 22, wherein the feedback
controller has less authority to adjust the engine speed during
deceleration of the engine speed than during acceleration of the
engine speed.
Description
FIELD
The present disclosure relates to marine propulsion systems for use
on marine vessels, and more specifically to systems and methods for
setting an engine speed of an internal combustion engine of a
marine propulsion device in a marine propulsion system.
BACKGROUND
U.S. Pat. No. 6,234,853, hereby incorporated by reference herein,
discloses a docking system which utilizes the marine propulsion
unit of a marine vessel, under the control of an engine control
unit that receives command signals from a joystick or push button
device, to respond to a maneuver command from the marine operator.
The docking system does not require additional propulsion devices
other than those normally used to operate the marine vessel under
normal conditions. The docking or maneuvering system of the present
invention uses two marine propulsion units to respond to an
operator's command signal and allows the operator to select forward
or reverse commands in combination with clockwise or
counterclockwise rotational commands either in combination with
each other or alone.
U.S. Pat. No. 8,762,022, hereby incorporated by reference herein,
discloses a system and method for efficiently changing controlled
engine speed of a marine internal combustion engine in a marine
propulsion system for propelling a marine vessel. The system
responds to the operator changing the operator-selected engine
speed, from a first selected engine speed to a second-selected
engine speed, by predicting throttle position needed to provide the
second-selected engine speed, and providing a feed forward signal
moving the throttle to the predicted throttle position, without
waiting for a slower responding PID controller and/or overshoot
thereof, and concomitant instability or oscillation, and then uses
the engine speed control system including the PID controller to
maintain engine speed at the second-selected engine speed.
U.S. Pat. No. 8,777,681, hereby incorporated by reference herein,
discloses systems for maneuvering a marine vessel that comprise a
plurality of marine propulsion devices that are movable between an
aligned position to achieve of movement of the marine vessel in a
longitudinal direction and/or rotation of the marine vessel with
respect to the longitudinal direction and an unaligned position to
achieve transverse movement of the marine vessel with respect to
the longitudinal direction. A controller has a programmable circuit
and controls the plurality of marine propulsion devices to move
into the unaligned position when a transverse movement of the
marine vessel is requested and to thereafter remain in the
unaligned position after the transverse movement is achieved.
Methods of maneuvering a marine vessel comprise requesting
transverse movement of the marine vessel with respect to a
longitudinal direction and operating a controller to orient a
plurality of marine propulsion devices into an unaligned position
to achieve the transverse movement, wherein the plurality of marine
propulsion devices remain in the unaligned position after the
transverse movement is achieved.
SUMMARY
This Summary is provided to introduce a selection of concepts that
are further described below in the Detailed Description. This
Summary is not intended to identify key or essential features of
the claimed subject matter, nor is it intended to be used as an aid
in limiting the scope of the claimed subject matter.
One example of the present disclosure is of a method for setting an
engine speed of an internal combustion engine in a marine
propulsion device of a marine propulsion system to an engine speed
setpoint. The method includes determining the engine speed setpoint
based on an operator demand and predicting a position of a throttle
valve of the engine that is needed to achieve the engine speed
setpoint. The method also includes determining a feed forward
signal that will move the throttle valve to the predicted position,
and after moving the throttle valve to the predicted position,
adjusting the engine speed with a feedback controller so as to
obtain the engine speed setpoint. An operating state of the marine
propulsion system is also determined, and depending on the
operating state, the method further comprises at least one of:
determining limits on an authority of the feedback controller to
adjust the engine speed; and determining whether the operator
demand should be modified prior to determining the engine speed
setpoint.
Another example of the present disclosure is of a marine propulsion
system for setting an engine speed of an internal combustion engine
in a marine propulsion device to an engine speed setpoint. The
system includes a throttle valve controlling an amount of air
provided to the engine and an input device for inputting an
operator demand. An electronic control unit determines an engine
speed setpoint based on the operator demand, predicts a position of
the throttle valve that is needed to achieve the engine speed
setpoint, and determines a feed forward signal that will move the
throttle valve to the predicted position. A feedback controller
adjusts the engine speed so as to obtain the engine speed setpoint
after the throttle valve has been moved to the predicted position.
The electronic control unit determines an operating state of the
marine propulsion system. Depending on the operating state, the
electronic control unit further determines at least one of: limits
on an authority of the feedback controller to adjust the engine
speed; and whether the operator demand should be modified prior to
determination of the engine speed setpoint.
BRIEF DESCRIPTION OF THE DRAWINGS
The present disclosure is described with reference to the following
Figures. The same numbers are used throughout the Figures to
reference like features and like components.
FIG. 1 is a schematic illustration of a marine propulsion system
known in the prior art.
FIG. 2 is like FIG. 1, but shows a marine propulsion system
according to the present disclosure.
FIG. 3 is a schematic illustration of a marine vessel having two
marine propulsion devices, according to another example of the
present disclosure.
FIGS. 4-7 are schematic diagrams of systems and associated methods
according to several examples of the present disclosure.
FIG. 8 is a flow chart showing further details of a method
associated with the diagram shown in FIG. 7.
FIG. 9 illustrates a method for setting an engine speed of an
internal combustion engine in a marine propulsion device according
to the present disclosure.
DETAILED DESCRIPTION
In the present description, certain terms have been used for
brevity, clarity, and understanding. No unnecessary limitations are
to be inferred therefrom beyond the requirement of the prior art
because such terms are used for descriptive purposes only and are
intended to be broadly construed. Each of the examples of systems
and methods provided in the FIGURES and in the following
description can be implemented separately, or in conjunction with
one another and/or with other systems and methods.
Prior Art
FIG. 1 shows a marine propulsion system 10 having an internal
combustion engine 12 for propelling a marine vessel 14, e.g. by way
of propeller 16, in a body of water 18. Engine speed is set by the
operator of the marine vessel 14 by using an input device 20, such
as a throttle lever, joystick, or the like, to input an operator
demand. An electronic control unit (ECU) 22 receives the engine
speed command from the input device 20 and includes appropriate
read only memory (ROM) 24 and random access memory (RAM) 26 and a
processor for interpreting the engine speed command and processing
it with a feedback controller 28, such as a proportional integral
derivative (PID) controller or a PI controller. Feedback controller
28 outputs a control signal to input-output (I/O) interface 30,
which in turn supplies a control signal to internal combustion
engine 12, including throttle valve 32, which controls engine speed
according to throttle position. By way of control with the feedback
controller 28, the ECU 22 maintains engine speed at the
operator-selected engine speed.
In response to the operator changing the operator-selected engine
speed at input device 20 from a first-selected engine speed to a
second-selected engine speed, the ECU 22 sends a signal to move the
throttle valve 32 to a new position to attempt to set the engine
speed to the second-selected engine speed. However, this type of
system is subject to overshoot, particularly with large speed
changes, when attempting to set engine speed to the second-selected
engine speed in response to the noted change by the operator of the
selected engine speed at input device 20. To accommodate various
changes, including large changes, the feedback controller 28 is
provided with enough amplification gain to provide a desired
response time to accommodate the change in the first-selected
engine speed to the second-selected engine speed at input device
20. The higher the amplification gain, the quicker the response
time; however, higher gain makes the system 10 subject to more
overshoot and instability.
Present Disclosure
Referring to FIG. 2, in the present system, in response to the
operator changing the operator-selected engine speed at input
device 20 from a first-selected engine speed to a second-selected
engine speed (engine speed setpoint), a prediction is made as to
the position of the throttle valve 32 needed to provide the
second-selected engine speed setpoint. A feed forward signal is
then provided at 34, which feed forward signal bypasses feedback
controller 28, and moves throttle valve 32 to the predicted
throttle valve position. After movement of the throttle valve 32 to
the predicted throttle valve position, the feedback controller 28
corrects the position of the throttle valve 32 as needed so as to
obtain and maintain the engine speed at the second
operator-selected engine speed. Throttle valve 32 is therefore
moved to the predicted throttle position in response to the feed
forward signal at 34, without waiting for the input of the feedback
controller 28 to move the throttle valve 32, thereby decreasing or
eliminating any overshoot otherwise caused by the system. The
system of FIG. 2 thereby enables reduction of the amplification
gain of the feedback controller 28 otherwise needed to accommodate
the change from the first-selected engine speed to the
second-selected engine speed at input device 20, and instead
accommodates such change by the predicted throttle position
provided by the feed forward signal 34. The feedback controller
amplification gain need only be large enough to maintain engine
speed at the second-selected engine speed, without having to
accommodate the change from the first-selected engine speed to the
second-selected engine speed. The reduced amplification gain
provides enhanced stability of the feedback controller 28 and
reduces oscillation of the system.
The present disclosure therefore includes marine propulsion system
10 for setting an engine speed of an internal combustion engine 12
in a marine propulsion device 36 to an engine speed setpoint. The
system 10 includes a throttle valve 32 controlling an amount of air
provided to an intake manifold of the engine 12 and an input device
20 for inputting an operator demand. The input device 20 may
comprise any of a throttle lever, a joystick, a touchpad, buttons,
etc., as will be described with respect to FIG. 3, and the operator
demand can be in the form of a value read from a potentiometer, a
numerical value input via digital interface, or any other type of
input known to those having ordinary skill in the art.
Returning to FIG. 2, the ECU 22 determines an engine speed setpoint
based on the operator demand, predicts a position of the throttle
valve 32 that is needed to achieve the engine speed setpoint, and
determines a feed forward signal 34 that will move the throttle
valve 32 to the predicted position. The ECU 22 then outputs the
feed forward signal to a throttle valve actuator, such as a motor
geared to the throttle valve 32. A feedback controller 28 adjusts
the engine speed so as to obtain the engine speed setpoint after
the throttle valve 32 has been moved to the predicted position. The
present disclosure provides an advantage in that the ECU 22 is able
to determine the engine speed setpoint and the authority of the
feedback controller 28 based on a particular operating state of the
system 10. Depending on the operating state, the ECU 22 further
determines at least one of: (a) limits on an authority of the
feedback controller 28 to adjust the engine speed; and (b) whether
the operator demand should be modified prior to determination of
the engine speed setpoint. Doing so provides several advantages as
described herein below.
FIG. 3 illustrates a schematic view of a marine vessel 14 provided
with two marine propulsion devices 36a, 36b. It should be
understood that although the marine propulsion device shown in
FIGS. 1 and 2 is an inboard drive, and outboard drives are shown in
FIG. 3, the present disclosure applies equally to all types of
marine drives: inboards, outboards, stem drives, etc. Returning to
FIG. 3, each marine propulsion device 36a, 36b has a throttle valve
32a, 32b that controls an amount of air entering an internal
combustion engine (ICE) 12a, 12b of each marine propulsion device.
The internal combustion engines 12a, 12b are operatively connected
to propellers 16a, 16b by way of transmissions 38a, 38b. The
rotation of the propellers 16a, 16b by the internal combustion
engines 12a, 12b via the transmissions 38a, 38b produces thrusts
T1, T2, respectively. The direction of thrusts T1, T2 depends on a
direction of rotation of the propellers 16a, 16b as determined by
the transmissions 38a, 38b, and depends on a rotational angle of
the marine propulsion devices 36a, 36b about steering axes
extending vertically through each one of the respective marine
propulsion devices 36a, 36b.
The amount of air entering the intake manifolds of the internal
combustion engines 12a, 12b is controlled by the throttle valves
32a, 32b, which in one example are electronic throttle valves in
signal communication with the ECU 22. The ECU 22 may also be in
signal communication with the transmissions 38a, 38b in order to
control whether and in what direction the propellers 16a, 16b turn,
i.e. whether the marine propulsion device 36a, 36b is in neutral,
forward, or reverse.
The ECU 22 may include a memory (ROM 24, RAM 26, see FIG. 2) and a
programmable processor. As is conventional, the processor can be
communicatively connected to a computer readable medium that
includes volatile or nonvolatile memory upon which computer
readable code is stored. The processor can access the computer
readable code, and the computer readable medium upon executing the
code carries out functions as described herein below. In other
examples of the system 10, more than one control unit is provided,
rather than the single ECU 22 as shown herein. For example, a
separate control unit could be provided in order to interpret
signals sent from a helm 40 of the marine vessel, and separate
control units could be provided for each marine propulsion device
36a, 36b. It should be noted that the dashed lines shown in FIG. 3
are meant to show only that the various control elements are
capable of communicating with one another, and do not represent
actual wires connecting the control elements, nor do they represent
the only paths of communication between the elements. Further, the
communications shown herein could be wired (for example, via a
serially wired CAN bus) or wireless.
The helm 40 includes a number of user input devices, such as an
interactive video display 42, a joystick 44, a steering wheel 46,
and a throttle lever 48. Each of these devices inputs commands to
the ECU 22. The ECU 22 interprets these commands and in turn
communicates with the propulsion devices 36a, 36b, such as for
example to provide commands regarding the magnitude and direction
of thrusts T1, T2 produced by the propulsion devices 36a, 36b.
As mentioned above, the ECU 22 determines an operating state of the
marine propulsion system 10, and depending on the operating state,
determines at least one of: (a) limits on an authority of the
feedback controller 28 to adjust the engine speed; and (b) whether
the operator demand should be modified prior to determination of
the engine speed setpoint. Various different operating states and
the response of the ECU 22 to detection of one or more of these
operating states will now be described with respect to FIGS. 4-8.
At the outset, it is worth noting that the system 10 can be in more
than one operating state at once, and that the systems and methods
described with reference to FIGS. 4-8 can be combined with one
another in various amalgamations.
Turning to FIG. 4, an example in which the operating state
comprises operation in an operator-selected control mode will be
described. According to this example, the same feedback controller
28 is used for each operator-selected control mode in a plurality
of operator-selected control modes in which the marine propulsion
system 10 may be operated. In this example, the ECU 22 selects the
limits on the authority of the feedback controller 28 based on the
particular operator-selected control mode in which the system is
currently operating. By an "operator-selected control mode," the
present disclosure refers to any one of a number of control modes
for operating one or more propulsion devices 36 aboard the marine
vessel 14.
For example, a propulsion device 36 could be operated in a trolling
mode, in which the speed of the propeller 16 is reduced to
trolling-like speeds. The propulsion devices 36a, 36b could be
operated in an auto sync mode, in which a speed of a first internal
combustion engine 12a (the "peer" engine) of the marine propulsion
system 10 is synchronized to a speed of a second internal
combustion engine 12b (the "master" engine) of the marine
propulsion system 10. The system could be operated in a joysticking
mode, in which input from the joystick 44 is converted to a desired
magnitude and direction of thrust of the internal combustion engine
12, and in which the marine propulsion devices 36a, 36b can rotate
around their steering axes to effect directional changes, lateral
movement, or various other maneuvers for the marine vessel 14, as
described in U.S. Pat. No. 6,234,853, or U.S. Pat. No. 8,777,681,
which were incorporated by reference herein above. The system 10
could be operated in a helm demand mode, in which a position of the
throttle lever 48 determines a magnitude and direction of thrust of
the marine propulsion device 36, while a position of the steering
wheel 46 controls steering of the marine vessel 14. Other
operator-selected control modes include cruise control, in which
both engines 12a, 12b are provided with the same setpoint speed,
and launch control, in which an operator can select a desired
aggressiveness of the vessel's launch profile, as described in U.S.
Pat. No. 7,214,110, or in U.S. patent application Ser. No.
14/104,291, filed on Dec. 12, 2013, both of which are hereby
incorporated by reference herein. Various other modes that provide
special features for operation of the marine propulsion system 10
could also be provided, and the control modes described herein are
not limiting on the scope of the present disclosure.
As mentioned above, the limits on the authority of the feedback
controller 28 to adjust the engine speed depend on the
operator-selected control mode, as shown by the diagram of FIG. 4.
At box 50, the operator inputs a helm demand, for example by
manipulating an input device 20. The operator may additionally or
alternatively select a control mode using the input device 20, as
shown at box 52. As described herein above, the control mode can be
any of a joysticking mode, auto sync mode, trolling mode, etc.
Because the same feedback controller 28 is used for each control
mode and because some marine propulsion systems can be operated in
more than one control mode at once, the ECU 22 next determines at
box 54 which control mode's gains, limits, and setpoint source
should be used to control the speed of the engine 12 based on a
hard-coded or calibratable priority of the control modes. For
example, the system 10 may be in both cruise control mode and auto
sync mode at the same time, but because cruise control mode and
auto sync mode may be provided with different PID gains, limits,
and engine speed setpoints, it is necessary to determine which
gains, limits, and setpoint source will be used to control the
engine speed. In one example, cruise control mode and launch
control mode have priority over both auto sync mode and helm
control mode, and auto sync mode may have priority over helm
control mode. Prioritizing cruise control mode over auto sync or
helm control mode is important because in auto sync mode, the peer
engine may hunt around to match the speed of the master engine.
This is to be avoided when the system is in cruise control mode,
and both the peer and master engine are provided with the same
engine speed setpoint already.
After the priority of one control mode over another is determined
at box 54, the engine speed setpoint corresponding to the
operator's demand and the prioritized control mode is looked up at
box 56. In one example, a given operator demand will correspond to
a given engine speed setpoint no matter which control mode is
prioritized. The engine speed setpoint is thereafter sent to a
summer 58 as well as to box 60, where a lookup table or other map
is used to determine the feed forward signal 34. The feed forward
signal 34 is passed through a summer 62 to move the throttle valve
32 to the predicted position, as shown at box 64. At box 66, the
actual (current) engine speed is read, for example using a
tachometer, and the actual speed is fed back to the summer 58.
Summer 58 outputs a difference between the engine speed setpoint
determined at box 56 and the actual engine speed determined at box
66, and inputs this to the feedback controller 28.
Meanwhile, the PID gains and limits are determined at box 68, which
PID gains and limits are also based on the prioritized control mode
determined at box 54. The PID gains include both a P-term gain and
an I-term gain. The gains may be determined based on the engine
speed setpoint and the engine speed error, determined at box 56 and
summer 58, respectively. The P-term gain is multiplied by the
engine speed error to output a P-term, as shown at box 70. The
I-term gain is multiplied by the integral of the engine speed error
to output an I-term, as shown at box 72. As shown in box 74, the
limits determined at box 68 are then used to limit the I-term. The
limits are provided as a maximum limit that the I-term cannot
exceed, and minimum limit that the I-term cannot fall below. In
other words, if the feedback controller 28 calculates an I-term at
box 72 that is outside the limits, the I-term is set at the limited
amount (i.e., at the maximum limit if the I-term is positive, or at
the minimum limit if the I-term is negative). In other examples,
the ECU 22 may look up limits to be applied to the P-term as well.
The (perhaps limited) I-term and P-term are then summed at summer
76, and provided as the output of the feedback controller 28.
(Although derivative control is not explicitly shown in FIG. 4, it
is to be understood that such control can be provided as well.) The
output of feedback controller 28 is supplied to summer 62, which
adds the output to the feed forward signal from box 60 in order to
adjust the position of the throttle valve 32, as shown at box
64.
As mentioned above, the i-term limits may be different for
different control modes. For example, it may be desirable to
provide maximum and minimum limits that are farther apart (thus
providing more authority to the feedback controller 28 to adjust
the speed of the engine) when operating in auto sync mode, where
the peer engine is attempting to match the speed of the master
engine, than when operating in helm mode. For example, it may be
that the master engine can achieve the setpoint speed with only 25%
throttle, while the peer engine may need much more throttle to
reach the setpoint speed. Opening up the 1-term limits allows the
feedback controller 28 more authority to affect the speed of the
peer engine by increasing its throttle up to the maximum limit
(which limit is particular to auto sync mode, and determined at box
68) until its speed matches the speed of the master engine. If
separate control units (and therefore separate feedback
controllers) are provided for each engine 12a, 12b, then the limits
on one feedback controller's authority can be changed without
affecting the limits on the other feedback controller's authority,
which is helpful when one engine is weaker than the other. Other
modes, such as joysticking, troll, cruise control, etc. may have
different limits (determined at box 68) and may therefore provide
different levels of authority to the feedback controller 28
depending on the control mode in which the system 10 is
operating.
The system 10 is also provided with a way to shift between
different limits on the authority of the feedback controller 28
when the operator switches from one control mode to another. In one
example, the ECU 22 waits to switch from a first operator-selected
control mode to a second operator-selected control mode until the
operator demand (input at box 50) is less than an upper demand
limit associated with the second operator-selected control mode.
For example, if the operator is switching from auto sync mode to
helm demand mode, and the current operator demand in auto sync mode
is higher than the limits particular to helm demand mode would
allow, the ECU 22 will wait until the operator has requested a
demand (at box 50) that would be achievable in the helm demand
mode, according to the limits particular to the helm demand mode,
before transitioning to the helm demand mode.
FIG. 4 therefore illustrates a system 10 in which the same feedback
controller 28 is used for any given operator-selected control mode
that might be chosen by an operator, and in which box 54 represents
a client selector that selects particular gains and limits for use
by the feedback controller 28 based on the particular
operator-selected control mode. Such a system minimizes the
complexity of having unique controllers for each operator-selected
control mode, with unique authorities and gains for each mode. The
system 10 therefore decreases the possibility that something is
missed during calibration because the calibrator will not have to
calibrate many unique governors, some of which may have been
sequential in the previous state of the art. In the present system,
only one feedback controller 28 is always active, so there is no
need to initialize or reset I-terms, to ramp P-terms, etc. Instead,
with box 54 acting as a client selector, the client selector
determines priority of one control mode over another based on a
combination of hard-coded and calibratable thresholds. Thereafter,
the client selector provides only one engine speed setpoint source
and only one set of PID gains and maximum and minimum limits for
use by the ECU 22.
FIG. 5 illustrates an example of the system 10 in which the
operating state comprises operation in a joysticking mode, in
which, as described above, a direction and magnitude of thrust of
the marine propulsion device 36 are determined based on a position
of a joystick 44. The below description of FIG. 5 also applies to
operation of the system in any operating mode where commands to the
ECU 22 are interpreted as joystick commands, such as electronic
anchoring or commands input via a touchpad. As shown at box 50, the
operator inputs a helm demand, in this example, by manipulation the
joystick 44. As the operator does so, he is not necessarily
thinking in terms of providing an engine speed setpoint to the
system 10. Rather, he is thinking in terms of a particular thrust
that he would like the marine propulsion devices 36a, 36b to
provide. For example, if the operator pushes the joystick further
in a forward direction, he would like the marine propulsion devices
36a, 36b to provide increasingly more thrust in the forward
direction. If he manipulates the joystick to one side or another,
he is requesting that the marine propulsion devices 36a, 36b
provide thrust to propel the marine vessel 14 sideways. In some
cases, depending on the way the operator manipulates the joystick,
the marine propulsion devices 36a, 36b may even provide thrusts in
different directions from one another. For example, as described in
the above-referenced joysticking patents, marine propulsion device
36a may provide a thrust in a forward direction while marine
propulsion device 36b provides a thrust in a reverse direction.
However, because marine propulsion devices 36a, 36b have different
efficiencies when they are operating in forward gear versus in
reverse gear, and because the marine propulsion devices have been
calibrated to provide particular thrusts based on a particular
movement of the joystick, the gear ratio and pitch of the
propellers 16a, 16b on the marine propulsion devices 36a, 36b can
affect the response of the system. If the operator demand input by
the joystick 44 is mapped to an engine speed setpoint using a map
that was calibrated for a propeller with a different pitch and/or
gear ratio, this may cause very low pitch propellers to seem to
lack authority, while high pitch propellers may seem overly
aggressive and potentially prone to blowing out. The present
inventors have realized that in order to eliminate the need for an
operator to close the loop between what he has requested and the
actual response of the system, the operator demand from the
joystick 44 could be modified prior to determining the engine speed
setpoint so as to account for one of a gear ratio and pitch of a
propeller 16 of the marine propulsion device 36 when the marine
propulsion system 10 is operating in the joysticking mode.
In one example, the ECU 22 is programmed such that it can modify
the operator demand based on gear ratio and/or pitch, as shown at
box 78. To do so, the ECU 22 may be programmed with a specific
torque multiplier that depends on the gear ratio of the marine
propulsion device 36 provided on the marine vessel 14. To account
for the specific gear ratio of the marine propulsion device, the
ECU 22 may modify the operator demand by multiplying it by the
torque multiplier programmed into the memory of the ECU 22 prior to
passing along this modified demand to box 56, where the ECU 22
would then determine the engine speed setpoint. The same method
could be used to modify the operator demand based on the pitch of
the propeller 16. Alternatively, rather than having a given
multiplier based on the propeller pitch programmed into the system,
the multiplier could be instead be determined from a lookup table
or similar map that accepts the joystick demand and pitch of the
propeller as inputs, and outputs a correction factor by which the
operator demand is to be multiplied prior to passing the modified
demand on to box 56, where the ECU determines the engine speed
setpoint.
Similar to FIG. 4, the engine speed setpoint is thereafter sent to
a summer 58, as well as used to look up a feed forward signal as
shown at box 60. The feed forward signal is passed through summer
62 and used to move the throttle valve, as shown at box 64. The
speed of the engine is then read at box 66 and provided to summer
58, which outputs a difference between the actual engine speed and
the engine speed setpoint from box 56. This difference is sent to
the feedback controller 28, which generates PID output on the
feedback, as shown at box 80. The PID output is sent to summer 62,
and the summation of the feed forward signal from box 60 and the
PID output from box 80 are used to adjust the position of the
throttle valve 32.
The system of the present disclosure therefore provides the
responsiveness and repeatability of an engine whose speed is
governed by a feed forward signal, with the intuitive feel of a
thrust response proportionate to operator demand input by a
joystick 44. It should be noted that while the method of the
present system is shown as being carried out by a general ECU 22,
the method could alternatively be carried out by a separate control
unit located at the helm 40 of the marine vessel 14.
FIG. 6 shows an example of the system 10 in which the operating
state comprises operation in a throttle-only mode, in which the
operator demand can be varied while the engine 12 is in neutral. To
enter the throttle-only mode, the operator of the marine vessel 14
may place the throttle lever 48 in neutral and thereafter select a
"throttle only" button, such as one provided on a track pad or on
the interactive video display 42. It should be understood that many
other methods could be used to enter the throttle-only mode, and
the above described method is merely one example. Once the system
10 is in the throttle-only mode, the operator may move the throttle
lever 48 to increase or decrease the speed of the engine 12 while
the transmission 38 is in neutral. This means that no torque will
be transmitted to the propeller 16 and the operator can therefore
increase or decrease the speed of the engine 12 without effecting
any movement of the marine vessel 14. Because the propeller 16 is
not spinning however, there is no load on the rotating engine 12,
and the engine 12 can be revved to very high speeds by very little
movement of the throttle lever 48. In prior systems, the ECU 22
would command cylinder cuts to control the maximum engine speed
that could be achieved while the marine propulsion device 36 was in
neutral. According to prior methods, the ECU would essentially
mis-fire the engine's cylinders when the engine speed exceeded a
particular threshold. If the engine speed exceeded the engine speed
threshold, the software would cut the cylinders, the engine speed
would fall below the threshold, and all cylinders would be
re-enabled. This prior method has drawbacks, one of which is that
the cylinder cut-based rev limiter is very loud and often alarms
the operator. Additionally, it can make other diagnostics, such as
neutral switch diagnostics, give false positives.
In contrast, the present system 10 limits engine speed by using the
throttle valve 32, which provides smooth engine speed control. The
present system does so by determining whether the operator demand,
input at box 50, exceeds a predetermined threshold while the marine
propulsion system 10 is operating in the throttle-only mode. If the
operator demand does not exceed the predetermined threshold, the
demand is passed through to box 56, where the engine speed setpoint
is determined. If the operator demand does exceed the predetermined
threshold, the present system modifies the operator demand by
capping it at the predetermined threshold, as shown at box 82,
prior to determining the engine speed setpoint. This capped value
is thereafter passed to box 56, where the engine speed setpoint is
determined. In one example, the operator demand is capped at a
value that would translate to an engine speed setpoint of 3500 RPM.
This method therefore catches an operator demand that would
otherwise cause the cylinder cut rev limiter to kick in prior to
that operator demand ever being passed through to determine an
engine speed setpoint or to look up the feed forward signal that
will move the throttle valve. The cylinder cut rev limiter method
remains in place to handle situations when the speed of the engine
12 needs to be cut very quickly, for example when the marine vessel
14 jumps a wave.
After the engine speed setpoint is determined at box 56, the
setpoint is sent through to the summer 58, as described herein
above. The engine speed setpoint is also sent to box 60, where the
feed forward signal is determined. In one example, the feed forward
signal is determined from a look up table or map that is the same
table or map used when the system is operating in forward gear. If
this is the case, the method then continues to box 84, where the
feed forward signal is multiplied by a fractional gain if the
system is in neutral. In one example, the fractional gain is 0.25
to 0.3. Multiplying the feed forward signal that would otherwise be
used if the system were in forward gear by a fractional gain
ensures that a large feed forward signal is not passed through
summer 62 to move the throttle valve, as shown at box 64, while
still providing the benefits of using a feed forward signal (as
opposed to merely PID control) described above with respect to FIG.
2. In an alternative example, no feed forward signal is provided,
and the system rather relies on the feedback controller 28
generating PID output on the feedback as shown at box 80 to achieve
the engine speed setpoint.
Turning now to FIG. 7, an example of the system 10 in which the
operating state comprises one of acceleration of the engine speed
and deceleration of the engine speed will be described. The system
10 shown in FIG. 7 provides a way to damp a response of the
throttle valve 32 during transient conditions, when the engine
speed is increasing or decreasing. A system that utilizes a feed
forward term to achieve an engine speed setpoint as shown in FIG. 2
provides excellent responsiveness when the engine speed is
increasing, because the PID control provided by feedback controller
28 can increase the position of the throttle valve 32 beyond the
required throttle angle during the transient. One problem with this
is that the same PID control can result in engine speed decreasing
transients that are too aggressive for drivability. For example, if
the feedback controller 28 commands the throttle valve 32 to shut
quickly to a low value (in response to the operator pulling back a
significant amount on the throttle lever 48) the actual engine
speed will drop below the desired setpoint, and the feedback
controller 28 will then have to command the throttle valve 32 to
open again to reach the setpoint. This dip and recovery of engine
speed taxes the system. The initial drop due to the feedback
control also translates to an abrupt boat speed change, which can
cause the operator to lunge forward.
The above-described effect is largely dominated by the proportional
control term (P-term) of the feedback controller 28. The system in
FIG. 7 therefore provides a method for limiting the P-term of the
feedback controller 28, although the I-term and/or D-term could
also be limited. Limiting the P-term in effect limits the authority
of the feedback controller 28 to adjust to the engine speed, and
therefore provides a good response during transients. The system 10
determines the maximum and minimum limits on the P-term by
calculating a demand delta, as shown at box 86, which will be
described herein below with reference to FIG. 8. The demand delta
is thereafter used to limit the P-term as shown at box 88, which
P-term was calculated by the feedback controller 28 as the error
multiplied by the proportional gain factor, as shown at box 70. If
the P-term exceeds a maximum, it is limited to the maximum; it if
it is lower than a minimum, it is limited to the minimum. The P
term is thereafter added at summer 76 to an I-term calculated at
box 72. The output of the feedback controller 28 from summer 76 is
passed to summer 62 and is combined with the feed forward signal 34
from box 60 to move the throttle valve, as shown at box 64.
Turning now to FIG. 8, the method of box 86 in FIG. 7 will be
further described. This method includes calculating a demand delta
between a current operator demand and a previous operator demand,
and using the demand delta and the engine speed setpoint to
determine the limits on the authority of the feedback controller 28
to adjust the position of the throttle valve 32. As shown at box
90, the method includes determining the current operator demand. In
one example, this is the helm demand input by the operator using
input device 20. The system's strategy starts in the disabled
state. In this state, the strategy filters the current demand using
a unique filter constant. In one example, the filter time constant
is 2 seconds. Filtering of the current demand allows the ECU 22 to
keep track of the filtered value so that the strategy can take a
difference (i.e., calculate the demand delta) when the operator
demand later changes. Otherwise, the software might not be able to
catch a change in the operator demand. The filtered demand value
therefore represents a previous operator demand that is stored by
the ECU 22. The strategy will then compare a new current demand
(after the demand changes) with the filtered demand value in order
to determine if the software should remain in the disabled state,
or if it should transition to a demand decreasing or a demand
increasing state.
As mentioned, the strategy may exit the disabled state and
transition into either a demand decreasing state or a demand
increasing state. At decision block 92, the system determines
whether the new current demand from input device 20 minus the
previous (filtered) demand is greater than a particular enable
threshold. If the answer is yes, then the system is in the demand
increasing state and the method continues to box 94, where the
previous demand is filtered to the current demand. In box 94, the
strategy stores the previous (filtered) demand from the disabled
state and calculates a difference between the filtered demand and
the current operator demand. This difference is essentially
filtered to zero as the filtered demand tends toward the current
operator demand. The filter constant used to carry out the
filtering in the demand increasing state is unique to this state,
and in one example is a shorter time constant than the filter
constant provided when the demand is decreasing. In one example,
the filter time constant is 0.25 seconds.
Returning to decision point 92, if the current demand minus the
previous (filtered) demand is not greater than the enable
threshold, the method continues to decision point 96, and
determines if the filtered demand minus the current demand is
greater than the enable threshold. Requiring that the difference be
greater than an enable threshold ensures that the remainder of the
strategy is only carried out if the demand undergoes a large
change, which could cause the above-described dip and recovery in
engine speed. If the answer is yes, this means that the system is
in the demand decreasing state, and the method continues to box 98,
where the filtered demand is filtered to the current demand. In the
demand decreasing state, the strategy stores the previous
(filtered) demand from the disabled state and calculates a
difference between the filtered demand and the current operator
demand. This difference is filtered to zero as the filtered demand
tends toward the current operator demand. The filter constant used
is unique to the demand decreasing state, and in one example is a
longer time constant than that used in the demand increasing state.
Filtering with a longer time constant essentially means that the
difference between the filtered and current demand remains greater
for a longer period of time, as the filter is applied more slowly.
In one example, the filter time constant is 3 seconds.
In one example, the filters applied in boxes 90, 92, and 96 are
first order exponential filters that operate according to the
equation: y(k)=a*y(k-1)+(1-a)*x(k), where x(k) is the raw input at
time step k; y(k) is the filtered output at time step k; and "a" is
a constant between 0 and 1. In one example, a=exp (-T/.tau.), where
.tau. is the filter time constant, and T is a fixed time step
between samples.
In either the demand increasing or demand decreasing state, after
the filtered demand is filtered to the current demand, as shown at
boxes 94 and 98, the method continues to boxes 100 and 102,
respectively, where the demand delta is calculated. The demand
delta equals the output of the continually filtered demand minus
the current demand. In other words, the demand delta represents the
remaining difference in demand before the filtering has been fully
carried out. Because the system filters the previous (filtered)
operator demand to the current operator demand, the demand delta
progressively decreases.
Returning to decision block 96, if the previous demand minus the
current demand is not greater than the enable threshold, then this
means that the system is in neither the demand increasing nor the
demand decreasing state, and therefore remains in the disabled
state. The system thereafter sets the demand delta equal to zero,
as shown at box 104.
Boxes 100, 102, and 104 thereafter lead to box 106, where the
demand delta is output. This demand delta is thereafter used to
determine the limits on the P-term, as shown at box 108. In one
example, this is done by inputting the demand delta and the current
user demand into a first lookup table or other similar map in order
to determine the minimum P-term limits and into a second lookup
table or map to determine the maximum P-term limits. The P-term
limits determined at box 108 are thereafter used to limit the
P-term, as shown at box 88 in FIG. 7.
In one example, the P-term limits tables provide the feedback
controller 28 with less authority to adjust the engine speed during
deceleration of the engine speed than during acceleration of the
engine speed. This helps prevent the above-described dip and
recovery problem, while still allowing aggressive acceleration. In
another example, the feedback controller 28 is provided with
increasingly more authority (as determined from the P-term limits
tables) to adjust the engine speed as the demand delta
progressively decreases while it is filtered out as described with
respect to boxes 94 and 98. This ensures that during the initial
stages of decreasing demand from the operator at the input device
20, the feedback controller 28 does not have a lot of authority to
adjust the engine speed, but as the demand delta decreases, the
feedback controller 28 is provided with increasingly more authority
to achieve the current demand requested by the operator. The
progressively decreasing demand delta and the engine speed setpoint
are used to determine the authority limits of the feedback
controller 28 during each iteration of control.
Other ways to exit the demand increasing or demand decreasing
states may be provided, such as if the ECU 22 determines that the
system is in an idle control state, in which the user has requested
a demand that is so low it is effectively an idle demand. In this
case, the system reverts to the disabled state and the idle
controller takes over. In other examples, once the demand delta has
decreased below a certain threshold, the system may exit the demand
increasing or demand decreasing state and return to the disabled
state, such that the actual engine speed can approach the engine
speed setpoint as determined by the operator demand input without
any limits.
It should be noted that the filtered demand kept track of according
to the method of FIG. 8 is not passed through as the demand that is
used to determine the engine speed setpoint. Rather, the filtered
demand is tracked for purposes of calculating the P-term limits, as
described with reference to box 108 of FIG. 8. Doing so provides
good steady state control and good transient performance in the
appropriate acceleration or deceleration directions.
Turning to FIG. 9, a further method according to the present
disclosure will be described. As shown at 902, the method includes
determining an engine speed setpoint based on an operator demand.
As shown at 904, the method includes predicting a position of the
throttle valve 32 of the engine 12 that is needed to achieve the
engine speed setpoint. As shown at 906, the method then includes
determining a feed forward signal that will move the throttle valve
32 to the predicted position. As shown at 908, after moving the
throttle valve 32 to the predicted position, the method includes
adjusting the engine speed with a feedback controller 28 so as to
obtain the engine speed setpoint.
The method also includes, as shown at 910, determining an operating
state of the marine propulsion system 10. Depending on the
operating state, the method further comprises at least one of
determining limits on an authority of the feedback controller 28 to
adjust the engine speed, as shown at 912, and determining whether
the operator demand should be modified prior to determining the
engine speed setpoint, as shown at 914. The results of these
determinations are applied to the determinations made at boxes 908
and 902, respectively.
In one example, the operating state comprises operation in an
operator-selected control mode, and the method further comprises
selecting the authority limits based on the operator-selected
control mode. The method may further comprise waiting to switch
from a first operator-selected control mode to a second
operator-selected control mode until the operator demand is less
than an upper demand limit associated with the second
operator-selected control mode. This example is described here and
above with respect to FIG. 4.
In another example, the operating state may comprise operation in a
joysticking mode, in which a direction and magnitude of thrust of
the marine propulsion device 36 are determined based on a position
of a joystick 44. In that case, the method may further comprise
modifying the operator demand prior to determining the engine speed
setpoint to account for one of a gear ratio and a pitch of a
propeller 16 of the marine propulsion device 36 when the marine
propulsion system is operating in the joysticking mode. This method
is described herein above with respect to FIG. 5.
In another example, the operating state comprises operation in a
throttle-only mode, in which the operator demand can be varied
while the engine 12 is in neutral. In this case, the method may
further comprise determining whether the operator demand exceeds a
predetermined threshold when the marine propulsion system is
operating in the throttle-only mode, and if so, modifying the
operator demand by capping it at the predetermined threshold prior
to determining the engine speed setpoint. This method may further
comprise multiplying the feed forward signal by a fractional gain
when the marine propulsion system is operating in the throttle-only
mode. This method is described herein above with respect to FIG.
6.
In another example, the operating state comprises one of
acceleration of the engine speed and deceleration of the engine
speed. In this example, the method may further comprise calculating
a demand delta between a current operator demand and a previous
operator demand, and using the demand delta and the engine speed
setpoint to determine the authority limits. The method may further
comprise filtering the previous operator demand to the current
operator demand such that the demand delta progressively decreases,
and using the decreasing demand delta and the engine speed setpoint
to determine the authority limits. The method may further comprise
providing the feedback controller with less authority to adjust the
engine speed during deceleration of the engine speed than during
acceleration of the engine speed. The method my further comprise
providing the feedback controller 28 with increasingly more
authority to adjust the engine speed as the demand delta
progressively decreases. This method is described herein above with
respect to FIGS. 7 and 8.
In the above description, certain terms have been used for brevity,
clarity, and understanding. No unnecessary limitations are to be
inferred therefrom beyond the requirement of the prior art because
such terms are used for descriptive purposes and are intended to be
broadly construed. The different systems and method steps described
herein may be used alone or in combination with one another and
with other systems and methods. It is to be expected that various
equivalents, alternatives and modifications are possible within the
scope of the appended claims.
* * * * *
References